audio restoration

Audio restoration


Optimize, restore and repair:
Our audio engineers offer different ways, but also different combinations of means, to reduce noise, reverb and hum, fix clicks and clipping, remove sibilant consonants, crosstalk and noise from vocal pick-ups, homogenize sounds and ambiences and much more. Each tool and each treatment is part of a large active and dynamic ecosystem that are audio engineers are continuously improving to provide you a perfect result.

Record restoration: repairing sound defects
When a sound recording or recording is degraded, it is possible to partially restore its original acoustic properties. This operation is called audio restoration, audio cleaning or audio repair. We use audio restoration to restore its former glory to an old recording on cassette, magnetic tape or vinyl. But it is especially in the field of sound post-production that it is essential today. Let’s see in detail what the audio restoration possibilities are.

The sound engineer in charge of this process, commonly called a sound engineer, is mainly in charge of capturing; in a clean and optimal way, the dialogues, environments, room tones (room tones), and any action that is carried out in front of the camera; taking into account the continuity in the intent and timbre of the voice, as well as possible changes in ambient sound.

In order to increase the expressive potential of an audiovisual work, it is necessary to have a direct sound that is as clear as possible, which affects a better quality of the final product.

Outdoor sounds recording
Recording sound outdoors can be a complex situation. There are factors that make it necessary to prepare for what may occur depending on the location: the streets of the city, a school, the countryside, the forest, a park, etc.

Indoor sounds recording
Recording sound indoors is somehow a more controlled task; but it requires certain important care to take into account; how to find the best location for the power plant if it exists, so that the noise it produces does not interfere with the sound capture. It is convenient to check doors, windows or other holes and seal them so that unwanted noises do not leak. Also, whenever possible, turn off electrical appliances that generate noise: such as refrigerators, freezers, televisions, etc. and, although it seems obvious, ask everyone on set to be quiet during the recording.

Other sounds recording cases
There are other issues that can occur with spaces when recording direct sound indoors related to acoustics, such as reverberations and resonances. It is important to know that these problems can be solved with the help of absorbent materials, fabrics and/or foams that can be adapted to the set or placed in places on the set not reached by the camera.

Another difficulty that arises regularly has to do with the lighting, which sometimes does not leave space to bring the boom closer to the actors without creating shadows. Those responsible for the sound must be present during the rehearsals of the movements on stage, at the moment when the lighting technicians are illuminating and, if possible, carry out tests and suggest the need for space to carry out the work.

During the direct sound recording process, unfavorable conditions or habits may arise for obtaining a clean sound. There are a number of factors that influence poor sound capture, among others we can mention:

• Not having suitable technical equipment: microphones, cables, consoles; in necessary quantity and quality.
• Not having trained sound technicians and microphone operators.
• Choose locations putting the image before the sound, without taking into account that many times the environment cannot be controlled: neighboring places, buildings, vendors, neighbors, nearby schools, etc.
• Inadequate coordination with the direction of photography, lighting design, lighting, breaking the balance between photography and sound.
• Arranged time standards that are insufficient and conspire against the quality of the audiovisual, both in the production stage, as well as in the editing and post-production stage.
• Insufficient budget for the realization of the audiovisual.

It’s difficult and expensive to get clean sounds while recording scenes, whether indoors or outdoors.

Many people are involved in the recordings, there is a lot of equipment from the shooting or from outside that emits unwanted sounds that contaminate the original sound record, among other factors, that damage and darken the quality of the sound captured.

The importance of capturing direct sound in filming tends to be underestimated, trusting that it can be fixed in post-production, however, the only thing that is achieved is to delay this process, because when obtaining a deficient sound, it is necessary to proceed to restore the deficiencies detected during post-production, lengthening this stage and using the time assigned to audio restoration instead of devoting it to artistic creation.

To avoid all of the above about recording live sound during filming, the following can be considered:

Have specialized personnel who know the equipment and techniques necessary to make a good recording. The ideal human team for a professional shoot should be two people, the head of sound and the microphone operator. The sound manager is in charge of listening to what the microphone operator captures and guides him to obtain a good take. However, a person who has experience in both roles can perform them without any problem.

Not every microphone is good for capturing direct sound. Most commonly, microphones with a cardioid directionality pattern or its supercardioid and hypercardioid variants are used. These types of microphones are very directional, which allow sound to be captured from the direction in which they are placed very precisely, since their sensitivity in areas other than this point is minimal.

You have to take advantage of the moments when the scene is rehearsed or the script is reviewed before starting to record to adjust the sound input levels and not spend time only on this. To make a good adjustment of levels, the microphone should be placed at the most suitable distance that the scene allows in relation to the actors, and make sure that the microphone is on axis. The input signal level should never saturate, however, currently there are tools to try to rectify the distortion caused by saturation, depending on the level of the error, it can be improved or eliminated. There is no standard value for input levels, the dynamics of the scene must be taken into account.

Difficulties may be encountered when recording certain scenes. For example, in long shots, the more open the shot, the more difficult it is to get a good shot of dialogue or text. The solution to avoid dubbing in post-production is very simple. Once it has been assessed that the sound of the scene cannot be recorded for this reason, the actors are asked to interpret the script as faithfully as possible to the scene performed off camera. In this way, it is not necessary to depend on dubbing, but rather that scene can be directly assembled with the shots recorded later on the axis. This procedure is feasible if there is no other recourse.

The primary tool for recording sound has always been the microphone. Depending on its characteristics and its technical state, the results may be better or worse.

A part of the sound quality of an audiovisual material is conditioned by the quality obtained in direct sound. Those who capture the sound at the time of recording should take all the necessary precautions to avoid capturing unwanted sounds, monitor what is being recorded with headphones with a good response and acceptable volume, to distinguish well everything that the microphone picks up, control any noise that occurs during filming, which is only perceived if it is properly monitored.

The higher the quality of the recorded sound, the less need to practice audio restoration, less need for editing and post-production, and more content in ideal conditions with which to work and obtain a result superior to the existing one.



With many poorly captured sound recordings created in inadequate spaces, audio restoration has become essential to the editing and mixing processes. This translates into the possibility of having a variety of opportunities to improve the deficiencies of an audio signal.

Sound restoration is a fairly complex process and little research has been done in this field. Before restoring any files, you must preserve and maintain the primary source files, that is, you must never work on the original file. The restoration in this case, specifically of digital audio, is based on the study and/or analysis of possible errors that appear for different reasons in the captured sound and the processes that exist to correct them. It is necessary not to forget that during sound restoration the original audio must always be preserved, it is not known when to return to the primary record.

At present, with the use of digital technology, many of the deficiencies captured or appearing in the original audio can be eliminated without leaving evidence of their elimination. Audio restoration is a slow and subjective process that requires a certain degree of specialization and there are various strategies that the sound editing engineer or technician can carry out.

It’s a process that is usually carried out in two stages. In the first stage, possible errors appearing in the original files are identified and analyzed to carry out possible restorations, which depends on the tool that will be used by the technician in question. Regardless of the fact that there are specific tools designed to correct certain errors, it is valid to experiment and improvise. In the second stage we proceed to execute the actions and processes proposed.

It’s necessary to take into account some details about the restoration, in addition to being a slow process, it is surgical, requires a lot of practice and patience. The order in which the processes are implemented can affect the result, it should not be processed on a large scale, that is, run violent processes and expect to obtain positive effects.

Sound restoration has the power to attenuate or remove unwanted audio with precision and few side effects, restoration processes work best if subtle values are used to minimize the appearance of these effects, thus ensuring a more inventive result. Sound technicians or specialists look for quick ways forward, but attempting an admirable, artifact-free fix takes time, practice, and dedication. However, if this process is abused, you can end up with a product inferior to the original file.

In the sound files you can find disturbances of any kind: hisses, pops, clicks and reverberations captured on a non-acoustically treated film set. For all this, there are audio technology companies that offer tools for sound restoration, processing, and post-production.



We can meet different sound faults, here some examples:

Equalizer sound restoration: correcting spectral defects
The equalizer or EQ is the #1 tool in sound post-production. In mixing, sound design, mastering and sound restoration, it’s a bit like the Swiss army knife of the sound engineer. It attenuates or amplifies the different frequencies that make up a sound. In sound repair, it is mainly used subtractively, to attenuate annoying frequencies. Tonal sounds can thus be reduced, with marked harmonics such as buzzes, neon noises, electronic noises, whistles, etc.

The denoiser: reduce background noise
The denoiser (or noise reducer) is an algorithm that separates the useful signal from the background noise to attenuate the latter. It is a tool that has evolved enormously over the past twenty years. By nature, denoisers generate digital artifacts that can be devastating if the tool is misused. It therefore takes some experience and expert ears to find the best profit/loss balance.

Remove Reverb
Reverberation is the repetition of the same sound by acoustic reflection. Due to the popularization of sound recording equipment and its use by non-specialists, parasitic reverberation has become a frequent problem, which must absolutely be resolved at the time of recording.
In post-production, removing reverb is a real headache. It is therefore very difficult for an algorithm to separate the direct field from the reverberant field and the process generates artifacts that are very unpleasant to the ear (pumping, drying of the sound).
Our audio engineers will use several tools based on the principle of the denoiser which, however, will give correct results, and provide you sounds finely adjusted.

The Noise Gate
The noise gate or noise gate is a basic tool used to remove background noise. This is a dynamics processing effect that removes extraneous sounds below a certain volume, called the threshold. All weak sounds are thus eliminated: background noise, breathing, etc. Only problem, when the signal goes back above the threshold, the background noise also reappears.

Manual restoration
It is possible to manually restore the sound using an editor in the form of a spectrogram. Like a graphic designer in Photoshop, the sound engineer can erase, copy or paste small time and frequency areas of sound to remove certain specific defects. This method is tedious but gives very good results.



The quality of the sound recording:
The quality of a sound recording is essential and nothing replaces a good, well-placed microphone. Knowing about post-production and sound restoration allows on-set sound engineers to better anticipate problems on set.

For example, it can happen that a sound engineer will work on a commercial shoot in a large, almost empty room. In this room, the decoration team had built several small sets with several rooms. But the acoustics of the place, very reverberant, did not correspond to these decorations. As the budget did not allow post-synchronization to be envisaged, we will use directional microphones placed as close as possible to the actors and HF microphones, to favor the direct sound as much as possible. The cinematographer even agreed to let the microphone into the shot and erase it in post-production.
This allowed us to clean up the little residual reverberation in post-production to replace it with artificial acoustics adapted to the supposed places of the image. This subtle operation would have been impossible if the sound recording had not been careful, the restoration would only have served to save the understanding of the text and not to recreate an acoustic consistent with the image.

The myth of sound post-production
There is a fairly widespread belief that it is easier to fix sound than an image, for example. We sometimes hear people say: “we’ll see about that in the mix”. Sound restoration is very tedious, just like photo editing, video editing or architectural restoration. It’s rarely a good financial calculation to rush a recording and hope to restore it later.

However, I often receive requests for repair of sound recordings which do not present any difficulty in filming. In this case, I always advise, as a first intention, to redo the socket.

Restore with parsimony and know-how
The profit/loss balance is crucial in audio repair. While restoration tools are now relatively accessible to the general public, their use requires experience and an expert ear to judge the relevance of audio processing.

The damage from a failed restoration is often much worse than the problem itself.